左程云大厂算法刷题班—

第一题

leetcode37：解数独

public class 第一题08 {public void solveSudoku(char[][] board) {boolean[][] row = new boolean[10][10];boolean[][] col = new boolean[10][10];boolean[][] box = new boolean[10][10];initBoard(board,row,col,box);process(board,row,col,box,0,0);}private boolean process(char[][] board, boolean[][] row, boolean[][] col, boolean[][] box, int i, int j) {if (i == 9){return true;}int nexti = j == 8 ? i + 1 : i;int nextj = j == 8 ? j + 1 : 0;if (board[i][j] == '.') {int b = 3 * (i / 3) + j / 3;for (int k = 1; k < 10; k++) {if (!row[i][k] && !col[j][k] && !box[b][k]) {row[i][k] = true;col[j][k] = true;box[b][k] = true;board[i][j] = (char)(k + '0');if (process(board, row, col, box, nexti, nextj)) {return true;}row[i][k] = false;col[j][k] = false;box[b][k] = false;board[i][j] = '.';}}return false;}else {return process(board,row,col,box,nexti,nextj);}}private void initBoard(char[][] board, boolean[][] row, boolean[][] col, boolean[][] box) {for (int i = 0;i < 9;i++){for (int j = 0;j < 9;j++){if (board[i][j] != '.'){int num = board[i][j] - '0';int b = 3 * (i / 3) + j / 3;row[i][num] = true;col[j][num] = true;box[b][num] = true;}}}}
}

第二题

三个有序数组中，|X-Y| + |Y - Z| + |Z - X|最小的值


public class 第二题08 {public static void main(String[] args) {int[][] matrix = {{1,4,7},{2,5,9},{1,8,10}};int[] res = minRange(matrix);System.out.println(res);}public static int[] minRange(int[][] matrix){for (int[] arr : matrix){if (matrix == null || matrix.length < 1){return null;}}TreeSet<Node> treeSet = new TreeSet<>(new Comparator<Node>() {@Overridepublic int compare(Node o1, Node o2) {int res = ((o1.num - o2.num) == 0) ? (o1.toString().compareTo(o2.toString())) : (o1.num - o2.num);return res;}});int n = matrix.length;for (int i = 0;i < n;i++){treeSet.add(new Node(matrix[i][0],i,0));}int[] ans = new int[2];int mineln = Integer.MAX_VALUE;while (treeSet.size() == n){if (mineln > treeSet.last().num - treeSet.first().num + 1){mineln = treeSet.last().num - treeSet.first().num + 1;ans[0] = treeSet.first().num;ans[1] = treeSet.last().num;}Node poll = treeSet.pollFirst();if (poll.ownIndex < matrix[poll.arrIndex].length - 1){poll.ownIndex++;treeSet.add(new Node(matrix[poll.arrIndex][poll.ownIndex],poll.arrIndex, poll.ownIndex));}}return ans;}static class Node{public int num;public int arrIndex;public int ownIndex;public Node(int num,int arrIndex,int ownIndex){this.num = num;this.arrIndex = arrIndex;this.ownIndex = ownIndex;}}
}

第三题

leetcode781：森林中的兔子
思路：贪心

public class 第三题08 {public static void main(String[] args) {int[] answers = {1,1,2};int res = numRabbits(answers);System.out.println(res);}public static int numRabbits(int[] answers) {Arrays.sort(answers);int ans = 0;int cand = answers[0];int count = 0;for (int num : answers){if (num != cand){ans += ((count + cand) / (cand + 1)) * (cand + 1);cand = num;count = 1;}else {count++;}}return ans + ((count + cand) / (cand + 1)) * (cand + 1);}
}

第四题

leetcode50：Pow(x,n)
思路：快速幂

public class 第四题08 {public static void main(String[] args) {int res = pow(5, 7);double pow = Math.pow(5, 7);double myres = myPow(2,3);System.out.println(res + " " + pow);}public static int pow(int x,int n){int ans = 1;int cur = x;while (n != 0){if ((n & 1) == 1){ans *= cur;}cur *= cur;n >>= 1;}return ans;}public static double myPow(double x, int n) {double ans = 1;long newn = n;if (n < 0){x = 1.0 / x;newn = -newn;}while (newn != 0) {if ((newn & 1) == 1){ans *= x;}x *= x;newn >>= 1;}return ans;}
}

第五题

leetcode69： x 的平方根
思路：二分

public class 第五题08 {public static int mySqrt(int x) {if (x == 0){return 0;}if (x < 3){return 1;}long l = 1;long r = x;long ans = 0;while (l <= r){long mid = (l + r) / 2;if (mid * mid == x){return (int)mid;}else if (mid * mid < x){ans = mid;l = mid + 1;}else {r = mid - 1;}}return (int)ans;}
}

第六题

leetcode73：矩阵置零

public class 第六题08 {//空间复杂度为O(1)public static void setZeroes(int[][] matrix) {int n = matrix.length;int m = matrix[0].length;boolean first_row = false;boolean first_col = false;for (int i = 0;i < n;i++){if (matrix[i][0] == 0){first_col = true;break;}}for (int i = 0;i < m;i++){if (matrix[0][i] == 0){first_row = true;break;}}for (int i = 1;i < n;i++){for (int j = 1;j < m;j++){if (matrix[i][j] == 0){matrix[i][0] = 0;matrix[0][j] = 0;}}}for (int i = 1;i < n;i++){for (int j = 1;j < m;j++){if (matrix[i][0] == 0 || matrix[0][j] == 0){matrix[i][j] = 0;}}}if (first_row){for (int i = 0;i < m;i++){matrix[0][i] = 0;}}if (first_col){for (int i = 0;i < n;i++){matrix[i][0] = 0;}}}
}

第七题

leetcode152：乘积最大子数组
思路：动态规划——》动态规划空间优化O(1)

public class 第七题08 {//动态规划public int maxProduct1(int[] nums) {if (nums == null || nums.length < 1){return -1;}int n = nums.length;int[] dpmax = new int[n];int[] dpmin = new int[n];dpmax[0] = nums[0];dpmin[0] = nums[0];int max = nums[0];for (int i = 1;i < n;i++){int p1 = nums[i];int p2 = nums[i] * dpmax[i - 1];int p3 = nums[i] * dpmin[i - 1];dpmax[i] = Math.max(p1,Math.max(p2,p3));dpmin[i] = Math.min(p1,Math.min(p2,p3));max = Math.max(max,dpmax[i]);}return max;}//对动态规划进行空间优化——》O(1)public int maxProduct(int[] nums) {if (nums == null || nums.length < 1){return -1;}int n = nums.length;int dpmax = nums[0];int dpmin = nums[0];int max = nums[0];for (int i = 1;i < n;i++){int p1 = nums[i];int p2 = nums[i] * dpmax;int p3 = nums[i] * dpmin;dpmax = Math.max(p1,Math.max(p2,p3));dpmin = Math.min(p1,Math.min(p2,p3));max = Math.max(max,dpmax);}return max;}
}

第八题

leetcode172：阶乘后的零

public class 第八题08 {public static int trailingZeroes(int n) {int ans = 0;while (n != 0){ans += n / 5;n = n / 5;}return ans;}
}

第九题

leetcode190. 颠倒二进制位

public class 第九题08 {public static int reverseBits(int n) {n = (n >>> 16) | (n << 16);n = ((n & 0xff00ff00) >>> 8) | ((n & 0x00ff00ff) << 8);n = ((n & 0xf0f0f0f0) >>> 4) | ((n & 0x0f0f0f0f) << 4);n = ((n & 0xcccccccc) >>> 2) | ((n & 0x33333333) << 2);n = ((n & 0xaaaaaaaa) >>> 1) | ((n & 0x55555555) << 2);return n;}
}

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左程云大厂算法刷题班——08

第一题

第二题

第三题

第四题

第五题

第六题

第七题

第八题

第九题

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